Heating oxidation defects and control of galvanized round tube heating furnace

Oxidation refers to the process in which steel is subjected to the action of CO2, H2O, and O2 in the furnace gas during heating, resulting in the formation of iron oxide scales on the surface of the steel. Approximately 0.5% -3% of the steel is oxidized to form iron oxide scales (i.e. burned) every time it is heated, reducing the yield rate. At the same time, the accumulation of iron oxide scales at the bottom of the furnace can cause erosion of refractory materials and reduce the service life of the furnace. In addition, the thermal conductivity of iron oxide scales is much lower than that of metals, which affects the heating of steel billets.

Iron oxide scale is the oxidation product of steel, which is divided into three layers from the outside to the inside: Fe2O3, Fe3O4, and FeO. The experimental results show that Fe2O3 accounts for 10%, Fe3O4 accounts for 50%, and FeO accounts for 40%, with a melting point of approximately 1300-13501 ℃.

The factors that affect metal oxidation include heating temperature, heating time, and furnace atmosphere. The atmosphere inside the furnace and heating temperature have a significant impact, while the heating time mainly affects the amount of steel burned.

1. The oxidation of steel is not severe before the temperature of the steel pipe reaches 800 ℃, and the rate of change of the billet temperature above 800 ℃ is significantly accelerated;

2. The longer the high-temperature residence time of the tube blank in the high-temperature zone, the more severe the oxidation and burning damage;

3. The stronger the oxidizing atmosphere in the furnace, the more severe the oxidation and burning damage.

The proportion of the impact of the above three factors is generally 6:3:1.

The high-pressure water descaling on the galvanized round pipe heat treatment line will cause varying degrees of oxidation on the surface of the steel parts during the hot processing of steel, and form oxide scales with different thicknesses depending on the heating temperature and time. In order to improve the surface quality and dimensional accuracy of steel pipes, a high-pressure water descaling process is used during the hot rolling process to remove oxide scales.

During the heat treatment and heating process, oxide scale will also form on the surface of the steel pipe. Adding a high-pressure water descaling process has the following advantages:

1. Like the rolling process, the high-pressure water descaling process can significantly improve the surface quality of the steel pipe;

2. After descaling and removing the oxide scale from the steel pipe, the cooling of the steel pipe is uniform and the heat exchange is accelerated during quenching, which can reduce the deformation of the steel pipe during quenching and improve the cooling rate;

3. During the straightening process of steel pipes after heat treatment, the steel pipes generate significant frictional forces on the straightening rollers, causing roller wear. The presence of oxide scales on the surface of the steel pipes accelerates the wear process, while descaling can reduce roller wear;

4. Non destructive testing is required for steel pipes after heat treatment. If there is oxide scale on the surface, it will affect the testing effect, and in severe cases, the testing cannot be carried out. However, the descaling process can avoid this situation.